1. Field of the Invention
This invention relates generally to dispensers and more particularly to a method and apparatus for dispensing a product based on mass.
2. Description of the Prior Art
Dispensers that utilize a diluent to erode a product, such as a detergent, are well known. The product being dispensed is typically a solid product and can take the form of either a solid block of chemical, pellets or a cast product. One example of such a dispenser is found in U.S. Pat. No. 4,826,661 by Copeland et al. This patent discloses a solid block chemical dispenser for cleaning systems. The dispenser includes a spray nozzle for directing a uniform dissolving spray on to a surface of a solid block of cleaning composition. The nozzle sprays on the exposed surface of the solid block, dissolving a portion of the block and forming a product concentrate. This is just one example of a dispenser that uses a diluent and further is just one example of the type of product that may be dispensed. It is recognized that there are many different dispensers which utilize diluents to erode and dispense a portion of a product, which may have any number of forms.
Once the product is dispensed, it is often necessary to know how much of the product has been dispensed. There are at least two major types of systems that have been developed to determine the amount of product that has been dispensed. The first is based on the amount of time that the product is exposed to the diluent. While such systems are useful, the systems are more susceptible to changes depending upon the amount of product that is being exposed to the diluent, the pressure at which the diluent is supplied or the temperature at which the diluent is supplied. Therefore, in many applications, it is necessary to supply more product than what is actually required so it is known that a sufficient amount of product is supplied.
Another method that has been utilized is to test the conductivity of the concentrate solution to determine the amount of product that has been dispensed. Again, this system has its own unique problems such as the necessity of adding chemistry to the product to allow the dilute concentration to be tested. Further, the conductivity based dispensers typically require on/off cycling to achieve an asymptotic approach to the concentration set point. Conductivity is also influenced by product concentration as a function of temperature and total conductivity. Shielded cabling is often required for conductivity based dispensers.
The present invention addresses the problems associated with the prior art devices and provides for a method and apparatus for dispensing product based on mass.